“Marx, Karl. [1862] 1985. "Marx to Engels in Manchester, 18 June 1862." Pp. 380-381 in Karl Marx Frederick Engels Collected Works, Marx and Engels: 1860-1864. Moscow: Progress Publishers. "Source: MECW Volume 41, p. 380; First published: in Der Briefwechsel zwischen F. Engels und K. Marx, Stuttgart, 1913.”

Source: Wikiquote